When testing or repairing electrical power line distribution systems, it is often necessary to disconnect and reconnect an unenergized (cold) line from an energized (hot) line. Directly disconnecting a high voltage (generally, above 600 volts) hot line from a cold line will result in considerable arcing between the two lines when the connection is broken. This arcing is extremely dangerous and frequently creates sparks which are equally dangerous. The sparks are very hot, they can burn, and an associated flash is very bright and can blind or damage the eyes. Thus, at high voltages, it is necessary to handle the lines from a distance with special sticks to provide safe working conditions between the operator and the lines.
The arcing can also be destructive as it will melt, weld or otherwise destroy equipment. Furthermore, if the arc goes to ground or cross-phase, it is possible that an entire power loop will fail, resulting in a power outage for many customers. Thus, it is desirable to maintain a controllable electrical connection between a hot line and a cold line while they are physically being disconnected from one another. After the lines are separated, the electrical connection can be broken. This prevents arcing between the hot and cold lines. Inversely, it is desirable to first electrically connect separated hot and cold lines before physically connecting them together to prevent arcing as the lines are brought together.
A conventional portable vacuum switch, often called a Rabbit Box, has been used to connect and disconnect hot and cold lines. However, such a vacuum switch requires a considerable amount of covering insulating material in order to make it available to use in a transformer box. Further, these portable vacuum switches require 4-5 people to properly operate them and their use is not very time efficient. An additional concern is that use of these portable vacuum switches is not considered to be particularly safe. Because of these problems, it is often easier to simply deenergize an entire circuit loop prior to undertaking work on the distribution systems. This is undesirable as it interrupts service to everyone on the circuit loop.